It is often considered desirable to provide a lock mechanism that locks a pair of connectors together after they have been mated. Threaded nuts lying around round connectors are commonly used to lock two connectors together, but it is more difficult to use this approach in holding two rectangular connectors together, the rectangular connectors having a greater height than width. Also, it can be tedious to properly threadably engage and turn a nut. Sometimes, screws are provided at the top and bottom of rectangular connectors, but turning both screws is tedious, and if they are not turned together then the connectors can be misaligned and the contacts damaged. Furthermore, in rectangular connectors, a large number of wires or other conductors extend from the rear of the connectors, and make it difficult to have access to the area behind a connector. A locking mechanism, especially for rectangular connectors, which was obvious to operate and which could be operated in a simple matter from a location other than the rear of the connector at the wires extending from the connector, would be of value.